In a wireless communications system such as a mobile cellular communications system, a wireless local area network (WLAN), or a fixed wireless access (FWA) system, a communications node such as a base station (BS), an access point (AP), a relay station (RS), or user equipment (UE) has a capability of transmitting a signal of the communications node and receiving a signal from another communications node. Because a radio signal on a radio channel is greatly attenuated, compared with a transmit signal of the communications node, a signal from a communications peer end becomes very weak when the signal reaches a receive end. For example, in the mobile cellular communications system, a power difference between a receive signal and a transmit signal of a communications node reaches 80 dB to 140 dB or even more. Therefore, to avoid self-interference of a transmit signal to a receive signal of a same transceiver, generally, receiving and transmitting of radio signals are performed at different frequency bands or in different time periods. For example, in a frequency division duplex (FDD) system, different bands separated by a specific guard band are used for sending and receiving. In a time division duplex (TDD) system, different time periods at a specific guard interval are used for sending and receiving. Both the guard band in the FDD system and the guard interval in the FDD system are used to ensure full isolation between the receiving and the sending, and avoid interference caused by the sending to the receiving.
Different from an existing FDD or TDD technology, a wireless full-duplex technology supports simultaneous receiving and sending operations on a same radio channel. In this case, spectral efficiency of the wireless full-duplex technology is theoretically twice as much as that of the FDD or TDD technology. Obviously, the premise of implementing wireless full-duplex is to avoid, reduce, and cancel as much as possible strong interference (referred to as self-interference) caused by a transmit signal to a receive signal of a same transceiver, so that the strong interference causes no impact on correct receiving of a wanted signal.
FIG. 1 is a schematic block diagram of an interference suppression principle in an existing wireless full-duplex system. A DAC (digital-to-analog converter), an up-converter and a power amplifier that are on a transmit channel, a low noise amplifier (LNA), a down-converter and an ADC (analog-to-digital converter) that are on a receive channel, and the like are functional modules of an intermediate frequency unit in an existing transceiver. Self-interference cancellation on a transmit signal is completed by using units shown in the figure, such as a spatial interference suppression unit, a radio frequency front-end analog interference cancellation unit, and a digital interference cancellation unit.
As shown in FIG. 1, the digital interference cancellation unit uses a digital baseband signal of a transmitter as a reference signal, and adjusts the reference signal by using estimated parameters of a channel from a local transmit antenna to a local receive antenna, such as an amplitude and a phase, so that the reference signal is as close as possible to a self-interference signal element in a receive signal (specifically, a digital-domain receive signal obtained after down-conversion processing), and a local self-interference signal received by the receive antenna is cancelled in the digital domain.
As mentioned above, the self-interference signal cancellation in a digital baseband part is generally performed after down-conversion processing in the receiver. Therefore, performance of the self-interference cancellation is greatly affected by factors, such as a phase noise, on a radio frequency channel in the system. If the impact is not eliminated, the performance of the self-interference cancellation is greatly affected.
Therefore, it is expected to provide a technology that can improve performance of self-interference cancellation.